(3X^2+2X-8)^2-(X^2-2X-8)^2
=[(3X^2+2X-8)+(X^2-2X-8)][(3X^2+2X-8)-(X^2-2X-8)]
=(4X^2-16)(2X^2+4X)
=8X(X^2-4)(X+2)
=8X(X-2)(X+2)^2.
(3X^2+2X-8)^2-(X^2-2X-8)^2
=[(3X^2+2X-8)+(X^2-2X-8)][(3X^2+2X-8)-(X^2-2X-8)]
=(4X^2-16)(2X^2+4X)
=8X(X^2-4)(X+2)
=8X(X-2)(X+2)^2.